proteins

Question 1

primary structure (2m)

Answer 1

-its precise number, type and sequence of amino acids held together by peptide bonds in the polypeptide chain
-contains information for the protein’s folding into a specific shape

Question 2

secondary structure (2m)

Answer 2

-coils and folds into geometrically regular repeating structures, mainly α-helices and β- pleated sheets
-stabilised by hydrogen bonds between C=O and -NH bonds in the main chain of the polypeptide

Question 3

α-helix (2m)

Answer 3

-elastic and flexible
-makes one complete turn for every 3.6 amino acids
-formation of intramolecular hydrogen bonds between the O of the C=O group and the H of the -NH group of every fourth peptide bond

Question 4

β-pleated sheet (2m)

Answer 4

-flexible but not elastic
-intramolecular hydrogen bonds formed between the O of C=O group and the H of the -NH group
folded in patterns

Question 5

tertiary structure (2m)

Answer 5

-further bent, coiled and folded extensively to form a precise 3D conformation
-specific 3D conformation maintained by intramolecular hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic interactions between the R groups of amino acids

Question 6

quaternary structure (2m)

Answer 6

-aggregation of two or more polypeptide chains
- held together by intermolecular hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic interactions between the R groups of amino acids

Question 7

effect of temperature on proteins (3m)

Answer 7

-increasing temperature leads to an increase in kinetic energy so molecular motion of protein increases
- high heat disrupts the hydrogen bonds and hydrophobic interactions that maintain the secondary and tertiary structures of protein
-loss of specific 3D conformation of the protein, leading to denaturation

Question 8

effect of pH on proteins (3m)

Answer 8

-alters the ionic charge of the COO-(acidic) and the NH3+(basic) R groups of the amino acids
- ionic bonds and hydrogen bonds maintain the tertiary structures of the protein
- loss of 3D conformation of the protein, leading to denaturation

Question 9

haemoglobin

Answer 9

-hydrophilic R groups of amino acids on the surface of the molecule face outwards and interact with the aqueous medium, maintaining solubility of haemoglobin
- allows for mobility around the body and can bind and transport oxygen molecules that are dissolved in blood
- contains a prosthetic haem group with an Fe2+. binds a molecule of oxygen reversibly and allows oxygen to be readily released to respiring tissues
- due to its allosteric nature, undergo changes in conformation. binding of oxygen to one haem group facilitates the binding of oxygen to the other haem groups, facilitating easier binding and release of subsequent oxygen molecules

Question 10

disulfide bond (3m)

Answer 10

• strong covalent bond formed between the sulfhydryl (-SH) groups of two molecules of cysteine
• strongest of all the chemical bonds between the R groups
• can only be broken by reducing agents and not by heat/pH